Carbon brush



M- GUARNIER March 1, 1960 CARBON BRUSH Filed Sept. 30, 1957 fhx entor.Maurice Guarn/el," b R W His fl'tor'ney United States Patent CARBONBRUSH Maurice Guarnier, Schenectady, N.Y., assign'or to General ElectricCompany, a corporation of New York Application September 30, 1957,Serial No. 687,137

4 Claims. (Cl. 310-449) The invention described herein relates to carbonbrushes of the type used in dynamoelectric machines and moreparticularly to an improved combination of shunt and brush adapted foruse in atmospheres highly corrosive of bare copper conductors.

Conventional carbon brush structure consists of a cop per shunt rivetedor otherwise secured to a carbon body for conducting current to or fromthe commutator of a dynamoelectric machine. It is well known that when amachine having such a brush is operated in an atmosphere containingelements corrosive of the copper parts used in the brush, rapidcorrosion of the shunt wire takes place, thus destroying the brushbefore the useful life of -the carbon has been realized. The adverseeffects are particularly noticeable in steel mill and paper millapplications where the air is highly laden with sulphur and chlorinefumes and in order to eliminate the corrosive action on the copper partsincluding the shunt, attempt has been made to coat the shunt withsubstances resistant to attack by the corrosive ingredients.

The use of wire enamel has been suggested, but the primary disadvantageis that the enamel must be removed from areas of the shunt to permitsoldering of terminals and to secure firm electrical contact with rivetsutilized in securing the shunt to the carbon body of the brush.

The degree of enamel removal cannot be closely controlled so that anexcessive amount of bare wire is presented for attack by the chemicalconstituents. The applications found to be most successful are thosewherein the carbon shunt is coated with a metal, such as lead orcadmium, for example, but these substances also are attacked by thecorrosive elements in much the same manner as the copper but to a lesserdegree.

The primary object of my invention therefore is to provide a carbonbrush having a shunt coated with a resin for protecting the coppertherebeneath from attack by air-borne chemicals prevailing in industrialareas.

In carrying out my invention, I coat the individual wires comprising thebrush shunt with a resin capable of protecting the copper wiretherebeneath from air-laden chemicals not compatible with the copper,prior to attaching a small copper sleeve on the shunt at a pointequidistant the shunt ends. The shunt or wire with the sleeve fixedthereon is welded to a metallic clip adapted for connection to thecarbon body of the brush by means of rivets or other well known securingmeans. In a modification, the resin coated shunt is susceptible ofattachment directly to rivets incorporated in the carbon body. Heat isthen applied to the brush for melting the resin on the shunt at itspoint of attachment so as to achieve proper electrical connectionbetween the parts.

The subject matter which I regard as my invention is particularlypointed out and distinctlyclairned in the concluding portion of thisspecification. My invention, however, both as to organization and methodof operation, together with further objects and advantages thereof, maybest be understood by reference to the following descrip- Patented Mar.1, 1960 tion taken in connection with the accompanying drawings inwhich:

Figure 1 is a perspective view of a carbon brush including a carbon bodyand a shunt attached thereto by means of a clip installed on a centralpart of the brush;

Figure 2 is a view illustrating a copper shunt with a small coppersleeve fixed thereon equidistant the shunt ends;

Figure 3 illustrates the arrangement of parts after the shunt of Figure2 is welded to a clip;

Figure 4 is a view in elevation, partly in section, showing thearrangement of a rivet utilized for securing the clip to the carbonbody;

Figure 5 is a view in elevation illustrating a modification of the brushshown in Figures 1 through 4; and

Figure 6 is a view in elevation, partly in section, of the brush shownin Figure 5.

Referring now to the drawings wherein like reference charactersdesignate like or corresponding parts through out the several views,there is shown a carbon brush consisting of a carbon body 10 having aclip 12 secured thereto by means of a rivet 14 extending transverselythrough the carbon body. A coated copper shunt 16 having a terminal 18connected to the ends thereof, is provided with a copper sleeve 20 whichserves to facilitate the welding of the copper shunt 16 to clip 12 atthe point indicated at 22.

Many different types and variations of resin coatings are adapted forapplication to the carbon shunt 16 and one example found to be extremelysuccessful in practicing the invention disclosed herein is disclosed inthe copending patent application of D. W. Fox and A. F. Zavist, SerialNo. 588,557, filed May 31, 1956, and assigned to the same assignee asthe present invention. The invention of the Fox et al. applicationprovides for a polyester resin base composition which can convenientlybe removed to permit soldering, but which has the desirable physicalcharacteristics of the polyester resin base material and, in particular;its heat stability. More specifically, the invention of the applicationcomprises the method and the material resulting from the admixture of(1) a composition consisting essentially of the reaction product of (a)from about 25 to 56 equivalent percent of a lower dialkyl ester of amember selected from the class consisting of isophthalic acid andterephthalic acid and mixtures of such members, (b) from about 15 to 46equivalent percent of ethylene glycol, and (c) from 13 to 44 equivalentpercent of a saturated aliphatic polyhydric alcohol having at leastthree hydroxyl groups and (2) a polyurethane or polyisocyanate.

Another type of resinous coating found to be satisfactory consists of apolyvinylal resin, blended in solution with a diisocyanate to produce apolyurethane film.

The polyvinylal resins are produced by suitably c0rn bining an aldehydewith a partially or completely hydrolyzed polymerized vinyl ester. Amongthe aldehydes which may be used to make the polyvinylal resins areformaldehyde, acetaldehyde, propionaldehyde, butyraldehyde,benzaldehyde, etc. Among the polyvinyl esters one may use to make thepolyvinylal resins are, for instance, polyvinyl acetate, polyvinylpropionate, polyvinyl butyrate, etc. The properties of the polyvinylalresins may be varied through a wide range by varying the viscosity andthe extent of the hydrolysis of the polyvinyl during hydrolysis. Methodsfor preparing these polyvinylal resins are more particularly describedin Reissue Patent 20,430-Morrison et al., as well as Jackson and Hallpatent, 2,307,588, assigned to the sameassigneeas the present invention,which by reference are made part of the disclosures of the presentapplication. Application of the polyurethane film to the individualwires of the copper conductor produces a product capable of being bentand twisted without creating cracks or other openings in v Operation Inoperation, stranded conductor wire coated with a polyurethane film orresin of the type describedabove, for example, is cut to a predeterminedlength suflicient to permit convenient attachment of the brush and wireto a source of voltage supply. The thin copper sleeve 20 is looselyfitted on the stranded wire conductor at a point equidistant its ends.The wire with its sleeve 20 is then placed in the clip 12 and weldedthereto by a machine capable of providing pressure to squeeze the sleeveand wire tightly together while simultaneously passing suflicientcurrent through the sleeve, wire and clip to obtain a firm weldingconnection between these parts. During the welding operation, heatgenerated as a result of resistance to flow of electric current, issufficient to melt and volatilize the resin from the stranded conductorat those points immediately underlying the copper sleeve placed on thestranded Wire, while also carrying out a welding function. Such heat isnecessary to break down the insulating qualities of the resin andthereby obtain a clean electrical connection between the copper wire andthe copper sleeve. The clip 12 with its welded wire conductor is thenattached to the carbon body 1% by means of the rivets 14.

As is evident, the resin on the ends of the wire adapted for receivingthe terminal 18 also must be removed in order to obtain completeelectrical connection between the parts. This is accomplished byinserting the ends of the conductor wire into the terminal and thenapplying a large pressure to tightly clamp the terminal around the freeends of the coated wire and thereby achieve a firm mechanical connectiontherebetween. Removal of resin from the wire to permit transfer ofelectrtic current to the terminal is accomplished by dipping in a bathof molten solder. The heat thus trans mitted through the terminal to thecoated wire melts and volatilizes the resin and exposes the bare copperWire to the inner portions of the terminal. The wire and its attachmentsthus constitute the brush shun.

In lieu of using a solder bath, other heat sources may be utilized, suchas the use of sand heated to a high temperature, a salt solution, or agas flame, for example, issuing from an acetylene torch. It will benoted that the primary purpose of the heat is to destroy the resin onthe wire located within the terminal and any type of heat source may beresorted to that will efiectively carry out a heat transferringfunction.

The same principles are applicable to the embodiment shown in Figuresand 6, but instead of using the clip 12, the shunt 16 is wrappeddirectly around rivets 14. As the rivets are spun, the copper shunt isrigidly afiixed to the carbon body 10, thereby providing a firmmechanical connection therebetween. In order to effect removal of resinfrom the wire and thereby establish electrical connection between thebrush and wire, the brush is immersed in a bath of hot material, such assolder, having a temperature sufiicient'to -melt and volatilize theresin. Immersion is made only to a point where heat can be transmittedto the rivet to accomplish removal of the resin on those portions ofshunt in engagement with the rivets. The solder will not adhere to thecarbon brush so that upon its removal from the hath, no metallic partswill remain on the brush which would 4 thereafter serve to damage thecommutator or adversely effect operation of the machine.

It will be evident that many modifications and variations are possiblein light of the above teachings. The inventive concept embodied hereinis that of providing a combined carbon body and copper shunt coated witha resin resistant to the attack of chemicals in the atmosphere inindustrial areas. The process employed for establishing electricalconnection between the conducting parts is also unique in that removalof the resin need not be made until the parts are mechanically securedtogether.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a carbon brush adapted for use in corrosiveatmospheres comprising a carbon body having a clip secured to the oneend thereof, a shunt comprising a plurality of copper wiresindividually, coated with a polyurethane resin and assembled to form asingle conductor, a copper sleeve on said shunt equidistant its ends,welding means securing said sleeve and therefore said shunt to said clipso as to secure said shunt in intimate electrical and mechanical contactwith said clip, and thereby provide a carbon brush resistant to thecorrosive effects of air-laden chemicals.

2. The method of assembling a carbon brush comprising the steps ofcoating the individual wires of a stranded conductor with a polyurethaneresin, loosely mounting a copper sleeve on said conductor intermediateits ends, placing said conductor with its attached copper sleeve in abrush clip and applying pressure and heat to said copper sleeve and clipfor compressing said sleeve into intimate contact with said conductorwhile simultaneously welding said sleeve with its enclosed conductor tosaid clip whereby the heat imparted to said sleeve and wire is ofsufiicient value to melt and volatilize the resin on said conductor andthus obtain electrical contact between said sleeve and said conductor,and mounting said clip with its attached conductor to said brush.

3. The method according to claim 2 including the additional steps ofinserting the free ends of said resin coated conductor into an openingprovided in a terminal, compressing the ends of said terminal in rigidmechanical relationship with the ends of said conductor, and immersingsaid terminal in a heated medium having a temperature suflicient to meltand volatilize the resin on said wire so that when heat is transmittedthrough said terminal clip, the resin is removed, thereby providingelectrical contact between said conductor and said terminal.

4. The method of assembling a carbon brush comprising the steps ofcoating the individual wires of a conductor With a polyurethane resinand assembling said wires into a stranded conductor, looping a portionof said conductor equidistant its ends over a rivet provided in an outerend of a carbon brush body, spinning said rivets to rigidly affix saidconductor into firm mechanical relationship with said carbon body,immersing a portion of said carbon body up to the rivets in a heatedbath of solder having a temperature sufiicient to melt and volatilizethe resin between said rivets and conductor so as to achieve properelectrical connection between said brush and said conductor.

References Cited in the file of this patent UNITED STATES PATENTS2,250,156 Ferguson July 22, 1941 2,509,020 Stauffer May 23, 19502,531,392 Breslow Nov. 28, 1950 2,648,792 Wylie Aug. 11, 1953'

1. IN COMBINATION, A CARBON BRUSH ADAPTED FOR USE IN CORROSIVEATMOSPHERES COMPRISING A CARBON BODY HAVING A CLIP SECURED TO THE ONEEND THEREOF, A SHUNT COMPRISING A PLURALITY OF COPPER WIRES INDIVIDUALLYCOATED WITH A POLYURETHANE RESIN AND ASSEMBLED TO FORM A SINGLECONDUCTOR, A COPPER SLEEVE ON SAID SHUNT EQUIDISTANT ITS ENDS, WELDINGMEANS SECURING SAID SLEEVE AND THEREFORE SAID SHUNT TO SAID CLIP SO ASTO SECURE SAID SHUNT IN INTIMATE ELECTRICAL AND MECHANICAL CONTACT WITHSAID CLIP, AND THEREBY PROVIDE A CARBON BRUSH RESISTANT TO THE CORROSIVEEFFECTS OF AIR-LADEN CHEMICALS.